Technical Abstract:
A breeding program to develop improved germplasm for the US rainbow trout aquaculutre industry is being conducted at the USDA ARS National Center for Cool and Cold Water Aquaculture (NCCCWA). Feed efficiency and stress tolerance are two traits being targeted for improvement. Superior growth, efficiency and tolerance of stressful conditions ar highly desirable characters for production animals. This study was undertaken to evaluate the interactions among feed efficiency, growth and the stress hormone cortisol in individual fish from three distinct line of rainbow trout. In the first, in a 7 week study, feed efficiency was evaluated in strains of rainbow trout using "residual feed intake" (RFI) as the measure of feed efficiency. In RFI lower values indicate greater efficiency. Fish were housed independently to get acurate measures of feed intake and growth for individual animals. A significant strain effect for feed efficiency was demonstrated. In another series of experiments, the response of these same strains to confinement stress was evaluated by measuring plasma cortisol. Strain efficiency performance and cortisol levels in response to stress were correlated in these strains. To directly examine the interaction of cortisol and feed efficiency in individual rainbow trout, a third experiment was conducted in which the individuals from the strains previously evaluated were implanted with a slow releasing cortisol/oil mixture (100 mg/kg) or the oil vehicle alone and placed into independent 100L aquaria. Although RFI did not differ among the strains, the cortisol implant caused a significant impairment of efficiency. The most efficient individuals may not be the ones that best tolerate increased cortisol. This relationship may indicate an antagonistic interaction between efficiency and stress.